Certified Crop Advisor Western Region

Size of sand and its characteristics

.05mm to 2.0mm, lower CEC, lower water holding capacity

Size of silt

.002mm - .05mm

Size of Clay

less than .002mm

Define bulk density

the ratio of the mass of soil to its bulk volume. expressed in g/cm3

How does bulk density differ with soil texture

sandy soil has higher bulk density because has less overall pore space.

Bulk density ranges of sand

1.2-1.8 g/cm3

Bulk density range for silt and clay

1.0-1.6 g/cm3

How does bulk density affect soils and plant growth

Increased bulk density = more compaction, root growth impaired, aeration and waster infiltration impaired

How does bulk density affects the interpretation of nitrate levels

oxygen supply and mineralization are slowed. Dry soil sample below 100 degrees F with soil sample . Increase over time if soil is moist.

Soil structure

Arrangement of soil particles into groupings.

Soil aggregates

the groupings of soil particles

Different types of soil structure

granular, blocky, prismatic, platy

list benefits of well-developed aggregates

small particles clump together to form more macrospores = better infiltration, aeration, provides habitat for various microorganism, bulk density

how do soil organisms and soul organic matter affect soil strucutre

aggregation formed by physical and chemical processes.

Soil microorganisms excrete substances that act as cementing agents and bind soil particles together.

Fungi have filaments, called hyphae, which extend into the soil and tie soil particles together.

Roots also excrete sugars into the soil that help bind minerals.

How does soil management affect soil structure

Adding gypsum (Ca2+) = electrostatic attraction binds soil

tillage = breaks up aggregates, increases rates of decomposition reducing soil OM

Cover crops/manures build OM

How does exchangeable sodium affect soil aggregation and waste movement in soils

high NA+ concentration displaces Ca2+ in soil. Sodium cannot bind soil particles because it is a monovalent ion, which results in deflocualtion and reduced water infiltration. Makes leaching difficult

How does soil salinity affect soil aggregation and water

soluble salts. increase salinity but Na is a small fraction of cation no serious soul structure or drainage issues

How structure can affect root growth

poor structure, increases compaction, reduces rooting depth/accumulation of nutrients, drain poorly/waterlogged

How does soil organic matter (SOM) affect soil aggregation

increased OM increases aggregation through physical and chemical processes

SOM affect on water holding capacity and infiltration

increases pore space/network of pores allowing for infiltration and waster holding capacity. Like a sponge.

a 1% increase in OM, increases water holding capacity by how much

3,400 gallons per acre (3.7% increase)

SOM affect on Cation exchange capacity

increasing OM increases CEC because OM in negatively charged

How OM is related to temperature

increase in temp, results in rapid decomposition of OM. colder climates generally have higher OM %

Role of OM in pesticide movement

OM binds pesticides and can make them less active

cation exchange capacity

a measure of the soil's ability to hold positively charged ions.

List three ways to maintain OM

reduce tillage, cover crops, avoid soil compaction and keep proper ph

Importance of soil OM in nutrient management

CEC, mineralization C:N ratio, 3% of soil OM overturns each year

Define salt

any ionic compound whose cation comes from a base and it's anion comes from an acid

a user of irrigation water should know the effects that water quality and irrigation practices have on what (6 elements)?

salt content (salinity) of soil

sodium status (sodicity) of soil

rate of water infiltration

toxic element content of soil

soil nutrient status

plugging of microirrigation systems

define parts per million

1 part of salt to 1 million parts of water

define milliequivalents per liter

a measurement of charge concentration per liter

convert ppm to meq/l

ppm = equivalent weight x meq/l

Define saline soil

a soil containing enough soluble salts to interfere with plant growth, but not containing an excess of exchangeable sodium

Define salinity

the amount of salt dissolved in water

Define sodium absorption ratio (SAR)

ratio of sodium to the sum of calcium and magnesium, measured on the basis of cation charges

Define electrical conductivity

measure of the bulk salinity in soil (ECe) or water (ECw)

What is the formula for SAR

SAR= Na/Square root of Ca+Mg/2 (%)

Define total dissolved solids

the measure of bulk salinity, usually only used for water (PPM)

calculate how much salt is applied per acre foot of water?

salts applied in lbs = TDS x 2.72

how many gallons is an acre foot of water

326,000 gallons

Define exchangeable sodium percentage (ESP)

Percentage of cation charges represented by sodium

Formula for ESP

(Na/sum of base cations)x100

Electrical conductivity of a saline soil

greater than 4 ds/m

Exchangeable sodium percentage (ESP) of a saline soil

less than 15 %

pH of a saline soil

less than 8.5

Sodium absorption ratio (SAR) of a saline soil

less than 13

Define a sodic soil

sodium concentration high enough to adversely affect structure, while overall salt concentration is below saline threshold

Electrical conductivity of a sodic soil

less than 4 EC

pH of a sodic soil

greater than 8.5

Exchangable sodium percentage of a sodic soil

Greater than 15

Sodium absorption ratio of a sodic soil

greater than 13

Define a saline-sodic soil

overall salt concentration high enough to reduce crop growth, together with sodium concentration high enough to damage soil structure

EC of a saline-sodic soil

greater than 4 ds/m

Soil pH of a saline-sodic soil

less than 8.5

SAR of a saline-sodic soil

greater than 13

ESP of a saline-sodic soil

greater than 15

convert EC less tahan 5 ds/m to TDS

EC X 640

convert EC more than 5 ds/m to TDS

EC X 800

calculate the total pounds of dissolved salts applied per acre foot of water?

TDS x 2.72

Explain how growth stage of crops can affect its salt tolerance

Plants are less salt tolerant as seedlings, during transplanting

explain relationship between SAR and ESP

numbers are numerically similar, with ESP marginally higher.

at what ECw (ds/m) is there no,slight to moderate, and severe restriction of use in water quality for irrigation in regards to salinity

less than 0.7, 0.7 - 3, greater than 3

at what TDS (ppm) is there no, slight to moderate, and severe restriction of use in water quality for irrigation in regards to salinity

less tahn 450, 450-2,000, greater than 2,000

when SAR is 0-3 at what ECw is infiltration problems unlikely to occur and likely

unlikely = ECw is more than 0.6

likely = ECw is less than 0.3

at what SAR levels is sodium permeability and plant growth not a problem, slight, and severe

less than 3, 3 to 9, and 9

6 inches of water moving through soil will leach how much salt

50%

How soil salinity and Exchangable sodium interact to affect soil structure and waster infiltration/movement

A high ESP correlates to poor structure because sodium displaces calcium in soil aggregates. Sodium in monovalent ion and cannot act as a bridge for soil particles. Deflocculation occurs which slows water infiltration rate making it difficult to leach salts in soil profile

Techniques to improve a saline soil

leaching with high quality irrigation water that is lower in salt content. chemical amendments not usually needed. 6 inches of water will reduce salinity by 50%

Techniques to improve a sodic soil

increase the soluble calcium level to stabilize structure by adding gypsum. Ca in gypsum will dislodge sodium ions from cation exchange sites. Leach with high quality water. If soil has free lime (CaCO3) add acid or elemental sulfur. Acid dissolves the lime increasing Ca. Add soil OM/break up compacted layers. reducing the ph and bicarbonate content of water by adding sulfuric acid

how many tons of gypsum are equal to 1 ton of sulfur

5.37 tons

How to calculate leaching requirement (LR) (expressed as a percentage of applied irrigation)

LR= ECw/(5(ECe)-ECw).

ECw = salinity of irrigation water in ds/m

ECe = soil salinity threshold above which a crop yield will decline in ds/m

Why do CA soils increase in salinity overtime

Low humidity and long growing season result in evapotranspiration. Irrigation water. Salt removal by crop is only a portion of salt applied

How to manage salt accumulation in seeding zone

Crop Salt balance = amount of salt applied via irrigation and fertilizers with the amount removed by crop.

TDS= measure of bulk salinity in irrigation waster

Can Calculate TDS from ECw

acre foot of water = 326,000 gallons

total lbs. of dissolved salts applied per acre foot of water = TDS x 2.72

total lbs of dissolved salts appled per acre in of water = TDS x .22

Salt balance example with TDS

-30 in of water at 700 PPM

2.72/12 = .22

.22x30inches = 6.8

6.8x700 = 4,760 lbs

with reasonably good irrigation practices the salt content of the saturation extract of soil is about wha times greater than salt content of soil?

1.5 - 3

Explain the complications with irrigation management and saline soils

Efficient irrigation requires a low LR, which in turn requires high quality irrigation water.

As ECw approaches ECe (crop threshold), LR becomes unreasonably high. cant have efficient irrigation above 20%

@ LR of 30% ECw=ECe

Explain the challenge of salinity management and groundwater quality

N leaching

List the major ccation constitents of irrigation water

Ca, magnesium, sodium (and potassium)

List the major anion constitents of irrigation water

Cl, SO4 or SO4-S (sulfate sulfur), HCO3 (bicarbonate), CO3 (carbonate), NO3 or NO3- N (nitrate nitrogen), boron

Other four constituents of irrigation water outside of cations and anions?

pH, Total dissolved solids, Electrical conductivity, alkalinity

Units water quality is usually measured in

PPM (same as mg/liter) or milliequivalents per liter (meq/liter)

convert ppm of Ca to meq/liter

divide by 20

convert ppm of Mg to meq/liter

divide by 12

convert ppm of NA to meq/liter

divide by 23

convert ppm of Cl to meq/liter

divide by 35

Boron is always expressed in what value

PPM

convert NO3 from PPM to Meq/liter

divide by 62

convert NO3-N from PPM to meq/liter

divide by 14

convert NO3 to NO3-N

NO3-N = NO3/4.43

list chemical constituents that are commonly measured in irrigation water and I.d. which of these can cause plant toxicities

NO3-N (PPM) x .23 = lb N /acre inch - nontoxic

Na -toxic

Cl- toxic

B-toxic

where does Na accumulate

in stem and leaf tissues

at what Na levels is there no restriction, slight to moderate, and sever with surface irrigation of tree/vine

less than 70 ppm, 70-200 ppm, greater than 200 ppm

at what Na levels is there no restriction, slight to moderate, and sever with ssprinkler irrigation of vegetables

less than 115 ppm, 115-460 ppm, greater than 460 ppm

the lower the leaching fraction the higher or lower average root zone salinity

higher

at what Na levels is there no restriction, slight to moderate, and sever with ssprinkler irrigation of tree/vine

less than 70 for both no restriction and slight

at what Cl levels is there no restriction, slight to moderate, and sever with surface irrigation of tree/vine

less than 140 ppm, 140-350 ppm, greater than 350 ppm

at what Cl levels is there no restriction, slight to moderate, and sever with sprinkler irrigation of tree/vine

less than 100 ppm

at what Cl levels is there no restriction, slight to moderate, and sever with sprinkler irrigation of vegetables

less than 175 ppm, 175-700 ppm, greater than 700 ppm

Symptoms of Cl toxicity in plants

appears in leaves as interveinal chlorosis and marginal burning as toxicity becomes more severe.

Symptoms of born toxicity in plants

yellowing and marginal burning of leaves